JAD is a tile based Maze-RPG, using OpenGL for graphics and SDL for input and sound to be platform independent. It's a multi-level dungeon in the spirit of 'Eye of the beholder' with a little bit extension into the 3rd Dimension.

Atanks is a multi-platform Scorched Earth clone similar to the Worms series of games. Annihilate the other tanks to earn money, then spend it on bigger and better shields and weapons to wipe out the opposition.

Scrabble3D is a highly customizable Scrabble game that not only supports Classic Scrabble and Superscrabble but also 3D games and own boards. You can play local against the computer or connect to a game server to find other players.

A Game Boy Color emulator.
How I came to the conclusion that reverse engineering is harder than pretty much anything ever (creating or understanding something [complex] tends to be immensely easier than to poke at that something [given a very limited interface] in order to find out exactly how it works [emphasis on "immensely" {just pointing that out such as to not seem like a total moron given that the statement might otherwise seem rather obvious (just adding this last part to get nested brace type overflow)}]).